Process of cracking petroleum hydrocarbons



July 19, 1932. A. M. HoUGHToN 1,868,418

PROCESS` OF CRACKING PETROLEUM HYDROCARBONS Filed May s, 1927 CHA/M6672Patented July 19, 17932 PATENT OFFICE ALFRED M. HOUGHTON, OF WASHINGTON,DISTRICT F COLUMBIA, ASSIGNOR T0 GULF REFINING COMPANY, 0F PITTSBURGH,PENNSYLVANIA, A CORPORATION 0F TEXAS PROCESS OF CRACKING PETROLEUMHYDROCARBONS Application lcd May 3, 1927.

This invention relates to improvements in processes of crackingpetroleum hydrocarbons; and comprises cleaning the draw-off line of acracking still by admitting to the still 5 through the draw-off line aportion of the oil either on its way to the cracking Zone or immediatelyafter it has passed the cracking zone; all as more fully hereinafter setforth and as claimed.

Oil cracking processes now in use to a large extent involve heating theheavier hydrocarbon to be cracked in one Zone, delivering the heatedproducts to another Zone, removing and condensing vapors from the secondzone l5 and removing heavy uncracked oil and tarry residual petroleumhydrocarbons from the second zone. Sometimes the oil is heated in thefirst zone under conditions whereby there is substantially no conversionand is then delivered to the second Zone and maintained there as a bodyof oil While conversion takes place. In such a process there results alarge amount of heavy tarry and asphaltic hyd-ocarbons which graduallyaccumulate and which tend to clog the draw-off pipe. In one process nowin use to a large eX- tent the oil is heated in the first Zone to acracking and vaporization temperature and there substantially vaporizedand converted and the products o-f such heating are delivered to aseparating chamber from which the vapors are removed and from whichresidual oil is removed substantially as fast as it accumulates. In thisprocess there is a tendency for the drawoff line to become clogged byheavy hydrocarbons and asphaltic matter which acts as a binder. Attemptshave been made to keep the draw-off line clear of accumulation of theresidue by mes chanical scraping devices and the like but these are noteminently successful due to inherent disadvantages in the operation of amechanical device inside a pipe where high pressures prevail.

In accordance with my invention the oil from the heating zone isdelivered to the second zone in one of the known ways and the draw-offpipe from the second zone is kept open for continuous withdrawal ofresidue` After a time when there is a tendency for Serial N0. 188,490.

ing Zone is caused to travel to the second zone through the draw-offpipe. This oil being hot i and under high pressure and traveling at aconsiderable rate of speed forces out accumulation of solid and tarrymatters in the drawolf pipe and causes them to mingle with any oil inthe second zone. A minute or so of such purging the draw-off pipe isusually sufficient, whereupon the normal process is resumed. Should theclogging of the draw-olf pipe be occasioned by an undue accumulation ofasphalt binder this may be dissolved more readily by a distillate whichhas not undergone any substantial conversion and therefore I may forcethrough the draw-off line and into the second Zone some of the chargeoil before it has reached and passed through the first heating` Zone,this charge oil containing a quantity of reflux condensate.

The accompanying illustration shows one form partly in section andpartly in elevation of a cracking unit in which my process may beperformed.

' In the drawing l indicates the furnace heated by means of oil burnerslocated at 2 and having mounted therein a coil 3 to which the Oil to becracked is supplied. This oil may comprise charge oil which has beenused to scrub outgoing vapors from the second zone, as will behereinafter described. The heated oil passes from the coils 3 by meansof line 4L to the chamber 5 which is provided with the dephlegmator 6,baffle plates 7, and inlet for charge oil 8. At a low point the chamberis provided with continuous drawoff line l0 having continuation 10A.Vapors from the dephlegmatO-r are delivered by line 13 to the finalcondenser. The charge oil after scrubbing the vapors arising in theseparating chamber is delivered together with condensate by means oftrap l1 and line l2 to the inlet of the cracking coils by means of pump12-A. Pressure may be maintained past the reflux condenser or past thefinal condenser 9 by means of the valves 14 and 15 respectively and, ifdesired, the pressure may be released before the oil is delivered fromthe first zone to the separating chamber.

In addition to the connections described I r provide a valved line 17leading` from the dis 3f charge or cracking coils to the draW-oi line.Also in addition to the charge line leading to the zone of heating Ivprovide a line 18 communicating the charge line With the tar drawoii.These lines are properly valved so that 10 some or Vall of the highlyheated oil from the heating zone may be sent through the dravvoff lineinto the chamber or some or all of the charge oil may be sent throughthe draw-off line into the chamber. 19 indicates a sample 15 line Whichmay be used from time to time for the purpose of observing the characterof the ,draw-off andrQO indicates the charge line which may be used atthe beginning of an operation for filling the system.

kClogging of the draw-ofi" line is due to a largey extent to athickening or solidification of asphaltic or tarry hydrocarbons actingas a binder for the carbon; the thickening or solidification beingincident to a drop in temperature between the cracking Zone proper andthe separation chamber. By adding het oil ofthe same character, thisthickening or solidication is obviated and the Whole mass is made mobileenough for removal.

What I claim is: l. In an oil cracking process in Which the oil isheated in one zone and delivered to a Second zone from Which heavyresidue is Withdrawn through a draW-of line, the step which comprisescleaning the draw olif line by'intermittently forcing therethrough intothe second zone some or' the cracked oil directly from the first zone.

2. In an oil cracking` process in which the oil isheated in one Zone anddelivered to a second zone from which heavy residue is Withdrawn througha draweoif line, the improvement Which comprises, during the crackingprocess, intermittently forcing 4Q through the draw-off line in adirection opposed to the normal draw-ofi', a quantityot the oilimmediately as it leaves the rst zone.

8. In an oil cracking process in which the oil is heated in one zone anddelivered to a 59 secondv zone from which heavy residue is Withdrawnthrough a dravv-oi line, the improvement Which comprises intermittently,during the cracking process, forcing through the draw-ofi1 line in adirection opposed to the i?? normal draw-off, a quantity of oil directlyfrom the first zone.

f In testimony whereof, I have hereunto affixed my signature. 6o ALFREDM. HOUGHTON.

